The present invention relates to hydrogen storage alloy reversibly capable of storing and emitting hydrogen and having electric conductivity, a process for producing the hydrogen storage alloy, a hydrogen storage alloy electrode, a process for producing the hydrogen storage alloy electrode, and a battery.
Conventionally, a hydrogen storage alloy has been known which shows the general formula of AB5. A representative form of this hydrogen storage exhibits the hydrogen storage alloy showing a formula of MmNi5 in which xe2x80x9cAxe2x80x9d sites in the general formula of AB5 take xe2x80x9cMmxe2x80x9d, and xe2x80x9cBxe2x80x9d sites take Ni. xe2x80x9cMmxe2x80x9d means misch metal. In the above-mentioned hydrogen storage alloy showing the formula of MmNi5, a part of Ni is replaced by Mn, Co, Al, etc. to improve characteristic properties. Especially, the hydrogen storage alloy having the formula of MmNi3.55Al0.30CO0.75Mn0.4 is provided.
Also, Japanese Unexamined Patent Publication (KOKAI) 8-315,813 discloses hydrogen storage alloy which has a parent phase having a crystal structure of CaCu5 (=AB5) type, and a second phase having Ni and/or Co. According to this parent phase, when a ratio of the number of atoms of Mm ( misch metal ) is set at 1, (Ni+Co+Mn+Al) is set at 4.5-5.5 in a ratio of the number of atoms, in order to increase the degree of activation. This publication discloses that the second phase has the composition Mo (Nixe2x80x94Co)3.
Also, Japanese Unexamined Patent Publication (KOKAI) No.7-286,225 discloses another hydrogen storage alloy. This hydrogen storage alloy has a hydrogen storage alloy phase having a crystal structure of CaCu5, and a second phase which is mainly composed of chemical elements not including Mm (misch metal) and which is distributed in a insular shape. In this publication, when Mm is misch metal, the hydrogen storage alloy phase has the general formula of MmNixMy. Also, this publication discloses the hydrogen storage alloy phase having the formula expressed as 5.0xe2x89xa6(x+y)xe2x89xa65.5. In general hydrogen storage alloy, since stress is caused by expansion in storing hydrogen storage and by contraction in emitting hydrogen, the hydrogen storage alloy is micronized. However, the second phase, not including Mm and being dispersed in a insular shape, can decrease the stress to suppress the micronization of the alloy.
Japanese Unexamined Patent Publication (KOKAI) 8-315,813 discloses a hydrogen storage, alloy electrode for an alkaline storage battery. In this publication, the parent phase of this alloy has the general formula of Mmxe2x80x94(Nixe2x80x94Coxe2x80x94Mnxe2x80x94Al)X, in which xe2x80x9cXxe2x80x9d is expressed as 4.5xe2x89xa6xxe2x89xa65.5. This parent phase has the crystal structure of CaCu5, and it has a spherical shape or a particle shape exhibiting a chicken egg shape. In this alloy, the second phases are produced at particle surfaces of the hydrogen storage alloy to has a catalytic ability for storing and emitting hydrogen. The second phase is composed of intermetallic compound having a high-melting point and including Ni and/or Co.
Japanese Unexamined Patent Publication (KOKAI) 4-168,240 discloses another hydrogen storage alloy having the formula of ABx. According to this hydrogen storage alloy, the xe2x80x9cAxe2x80x9d site in the formula of ABx shows lantern or misch metal, and the xe2x80x9cBxe2x80x9d site shows at least one from the group of nickel, cobalt, aluminum, manganese, chromium, copper, and zirconium. Then, the range of xe2x80x9cXxe2x80x9d is set in the formula of 5.5xe2x89xa6xxe2x89xa66.5. This alloy can suppress micronization thereof caused by storing and emitting hydrogen. Japanese Unexamined Patent Publication (KOKAI) 4-168,240 discloses MmNi3Co2Al0.5Mn0.5 as the hydrogen storage alloy exhibiting the formula of Mmxe2x80x94(Nixe2x80x94Alxe2x80x94Coxe2x80x94Mn). However, when a ratio of the number of atoms of Mm is 1, a ratio of the number of atoms of Ni is as small as 3. As a result, it is insufficient to generate an electrically conductive network having good conductivity.
In industry, the battery with a negative electrode composed of hydrogen storage alloy has been provided. Generally, when this battery is used in room temperature, the ratio between internal resistance of the positive electrode and internal resistance of the negative electrode does not indicate a large difference. This shows fundamentally the following:
(internal resistance of positive electrode:internal resistance of negative electrode)=1:1
On the other hand, when the battery is used in low-temperatures, the internal resistance of negative electrode tends to relatively increase. Especially, when temperature is near 0xc2x0 C., the internal resistance of the negative electrode composed of hydrogen storage alloy considerably increases. This shows fundamentally the following: (internal resistance of positie electrode:internal resistance of negative electrode )=1.3 (3-3.5).
When the battery is used in low-temperatures, the negative electrode shows a relative increasing rate in the internal resistance to restrict a battery reaction. Also, when the battery is charged at a high speed, since an exothermic reaction is generated by the internal resistance, the high-speed charging is restricted in the battery. Therefore, for ensuring the high-speed charging, it is preferable that internal resistance is low in the electrode and in the battery. In each of the hydrogen storage alloys concerning the above-mentioned publications, the second phase, showing good conductivity and including Ni, does not form a conductive network state sufficiently. Therefore, each of the above-mentioned hydrogen storage alloys is insufficient in forming an electric conductive route composed of the second phase.
Concerning Japanese Unexamined Patent Publication 4-168,240, the conductive route composed of the second phase is also insufficient.
The present invention has been developed in view of the above-mentioned circumstances. It is therefore an object of the present invention to provide hydrogen storage alloy, a process for producing the hydrogen storage alloy, a hydrogen storage alloy electrode, a process for producing the hydrogen storage alloy electrode, and a battery; which can improve electrical conductivity to decrease internal resistance and to increase power in low-temperatures and which can improve high-speed charging.
(Invention of Hydrogen Storage Alloy)
{circle around (1)} Hydrogen storage alloy according to a first aspect comprises: (1) a main composition expressed by the formula of Mmxe2x80x94(Nixe2x80x94Alxe2x80x94Coxe2x80x94Mn); (2) a ratio of the number of atoms expressed by the formula of (Nixe2x80x94Alxe2x80x94Coxe2x80x94Mn) is exhibited as 5.5 less than (Ni+Al+Co+Mn)xe2x89xa69, and 3.5xe2x89xa6Ni, when Mm is set at 1 in a ratio of the number of atoms; and (3) an internal structure having a hydrogen storage alloy phase expressed by the general formula of AB5, and a second phase existing in the hydrogen storage alloy phase.
xe2x80x9cMmxe2x80x9d means misch metal. The misch metal means an aggregate of rare earth elements such as Ce and La.
According to the hydrogen storage alloy concerning the first aspect, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn) is 5.5 or less, the second phase showing good conductivity decreases relatively, a conductive network composed of the second phase is not sufficiently formed, and the internal resistance of the hydrogen storage alloy increases; therefore, not obtaining an effect that power is improved.
Meanwhile, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn) exceeds 9, the conductive network composed of the second phase increases excessively, the hydrogen storage alloy phase decreases relatively; therefore, not obtaining a sufficient ability in storing and emitting hydrogen. Considering the above-mentioned circumstance, the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn) can be chosen on occasion. In the hydrogen storage alloy concerning the first aspect, the lower limit of the total quantity of (Ni+Al+Co+Mn) can be, for example, 5.6, 5.7, 5.8, 6.0, 6.2, 6.6, 6.7, etc.: the upper limit of the total quantity can be, for example, 8.8, 8.6, 8.4, etc. According to the hydrogen storage concerning the first aspect, the reason for restricting 3.5xe2x89xa6Ni is that the second phase including Ni to have good conductivity is easily generated in a network state. In this case, the ratio of number of atoms of Ni can be, for example, 3.6, 3.7, 3.8, 3.96, etc. as the lower limit.
Hydrogen storage alloy according to the first aspect may preferably be expressed as follows: the whole composition is MmNi(3.55+a)Al(0.3+b)CO(0.75+c)Mn(0.4+d), and 0.5 less than x(=a+b+c+d)xe2x89xa64. The above-mentioned formula of MmNi(3.55+a)Al(0.3+b)CO(0.75+c)Mn(0.4+d) is the meaning of MmNi3.55+aAl0.3+bCO0.75+cMn0.4+d. A large letter may sometimes be used on occasion in the present specification in accordance with a printing machine.
The reason for restricting 0.5 less than x (=a+b+c+d)xe2x89xa64 is fundamentally the same as the above-mentioned reason. That is to say, when the xe2x80x9cxxe2x80x9d value is 0.5 or less, the second phase having good conductivity decreases relatively, the conductive network composed of the second phase is not sufficiently formed, the internal resistance of the hydrogen storage alloy increases, and the a power-improving effect is not sufficiently obtained. Meanwhile, when the xe2x80x9cxxe2x80x9d value exceeds 4, the conductive network composed of the second phase increases excessively, the hydrogen storage alloy phase decreases relatively; therefore, not obtaining a sufficient ability in storing and emitting hydrogen. Considering the above-mentioned circumstance, the quantity of xe2x80x9cxxe2x80x9d can be chosen on occasion. The alloy according to the first aspect can choose, for example, 0.6, 0.7, 0.8, 0.9, etc. as the lower limit of the quantity of xe2x80x9cxxe2x80x9d: it can choose, for example, 3.8 3.6, etc. as the upper limit of the quantity of xe2x80x9cxxe2x80x9d.
{circle around (2)} Hydrogen storage alloy according to a second aspect comprises: (1) a main composition expressed by the formula of Mmxe2x80x94(Nixe2x80x94Alxe2x80x94Coxe2x80x94Mnxe2x80x94Mo); (2) a ratio of the number of atoms expressed by the formula of (Nixe2x80x94Alxe2x80x94Coxe2x80x94Mnxe2x80x94Mo) is exhibited as 5.5 less than (Ni+Al+Co+Mn+Mo)xe2x89xa68, and 3.5xe2x89xa6Ni, when Mm is set at 1 in a ratio of the number of atoms; and (3) an internal structure having a hydrogen storage alloy phase expressed by the general formula of AB5, and a second phase existing in the hydrogen storage alloy phase.
According to the hydrogen storage alloy concerning the second aspect, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn+Mo) is 5.5 or less, the second phase showing good conductivity decreases relatively, a conductive network composed of the second phase is not sufficiently formed, and the internal resistance of the hydrogen storage alloy increases; therefore, not obtaining an effect that power is improved. Meanwhile, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn+Mo) exceeds 8, the conductive network composed of the second phase increases excessively, the hydrogen storage alloy phase decreases relatively; therefore, not obtaining a sufficient ability in storing and emitting hydrogen. Considering the above-mentioned circumstance, the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn+Mo) can be chosen on occasion. In the hydrogen storage alloy concerning the second aspect, the lower limit of the total quantity of (Ni+Al+Co+Mn+Mo) can be, for example, 5.6, 5.7, 5.8, 6.0, 6.2, 6.6, 6.8, etc.: the upper limit of the total quantity can be, for example, 7.8 7.6, 7.4, etc. According to the hydrogen storage concerning the second aspect, the reason for restricting 3.5xe2x89xa6Ni is that the second phase including a plenty of Ni to have good conductivity is easily generated. In this case, the ratio of the number of atoms of Ni can be, for example, 3.6, 3.7, 3.8, 3.96, etc. as a lower limit.
The whole composition of hydrogen storage alloy according to the second aspect may be expressed as follows: MmNi(3.55+i)Al(0.3+j)Co(0.75+k)Mn(0.4+l)Mo(m), and 0.5 less than (i+j+k+l+m)xe2x89xa63.
In the hydrogen storage alloy concerning the second aspect, the reason for restricting 0.5 less than (i+j+k+l+m)xe2x89xa63 is fundamentally the same as the above-mentioned reason. That is to say, when (i+j+k+l+m) is 0.5 or less, the second phase having good conductivity decreases relatively, the conductive network composed of the second phase is not sufficiently formed, and the internal resistance of hydrogen storage alloy increases; therefore, not obtaining the effect for improving power. Meanwhile, when (i+j+k+l+m) exceeds 3, the conductive network composed of the second phase increases excessively, the hydrogen storage alloy phase decreases relatively; therefore, not obtaining a sufficient ability of hydrogen storage and hydrogen emission. Considering the above-mentioned circumstance, the total quantity of ratio of the number of atoms of (i+j+k+l+m) can be chosen on occasion. In the hydrogen storage alloy concerning the second aspect, the total quantity of ratio of the number of atoms of (i+j+k+l+m) can be, for example, 0.6, 0.7, 0.8, etc. as a lower limit: it can be, for example, 2.9, 2.8, etc. as an upper limit.
{circle around (3)} Hydrogen storage alloy according to a third aspect comprises: (1) a main composition expressed by the formula of Mmxe2x80x94(Nixe2x80x94Alxe2x80x94Coxe2x80x94Mnxe2x80x94Cu); (2) a ratio of the number of atoms expressed by the formula of (Nixe2x80x94Alxe2x80x94Coxe2x80x94Mnxe2x80x94Cu) is exhibited by 5.5 less than (Ni+Al+Co+Mn+Cu)xe2x89xa67.0, and 4.0xe2x89xa6Ni, when Mm is set at 1 in a ratio of the number of atoms; and (3) an internal structure having a hydrogen storage alloy phase expressed by the general formula of AB5, and a second phase existing in the hydrogen storage alloy phase.
The hydrogen storage alloy according to the third aspect intends to ensure performance of hydrogen storage alloy, while reducing expensive Co (cobalt) as much as possible. Thus, Cu and Ni are mainly used instead of part of expensive Co. According to the hydrogen storage alloy concerning the third aspect, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn+Cu) is 5.5 or less, the second phase decreases relatively, the conductive network composed of the second phase is not sufficiently formed, and the internal resistance of the hydrogen storage alloy increases; therefore, not obtaining effect for improving power.
Meanwhile, when the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn+Cu) exceeds 7.0, the conductive network composed of the second phase becomes superfluous, and the hydrogen storage alloy phase decreases relatively not to obtain ability of hydrogen storage and hydrogen emission.
Considering the above-mentioned circumstance, the total quantity of ratio of the number of atoms of (Ni+Al+Co+Mn+Cu) can be chosen on occasion. The hydrogen storage alloy according to the third aspect can choose, for example, 5.6, 5.8, 6.0, 6.2, etc. as a lower limit of this total quantity: it can choose 6.8, 6.6, 6.4, etc. as an upper limit. According to the hydrogen storage alloy concerning the third aspect, the reason for restricting 4.0xe2x89xa6Ni is that the second phase having mainly Ni to show good conductivity is easily formed in a network state. In this case, the alloy concerning the third aspect can choose 4.2, 4.4, etc. as a lower limit of the number of atoms of Ni. According to the hydrogen storage alloy concerning the third aspect, since Ni is added instead of a part of Co, the lower limit of the quantity of Ni is larger than that of the second aspect.
According to the hydrogen storage alloy concerning the third aspect, the whole composition is expressed as follows: MmNi(3.95+p)Al(0.3+q )Co(0.4+r)Mn(0.45+s)Cu(0.10+t), and 0.3 less than (p+q+r+s+t)xe2x89xa61.8. The reason for restricting the formula of 0.3 less than (p+q+r+s+t)xe2x89xa61.8 is fundamentally the same as the above-mentioned reason. That is to say, when the total quantity of ratio of the number of atoms of (p+q+r+s+t) is 0.3 or less, the second phase having good conductivity decreases relatively, and the conductive network composed of the second phase is not sufficiently formed, and the internal resistance of the hydrogen storage alloy increases not to obtain the effect for improving power.
Meanwhile, when the total quantity of ratio of the number of atoms of (p+q+r+s+t) exceeds 1.8, the conductive network composed of the second phase becomes excessive, and the hydrogen storage alloy phase decreases relatively not to obtain a sufficient ability of hydrogen storage and hydrogen emission. Considering the above-mentioned circumstance, the total quantity of ratio of the number of atoms of (p+q+r+s+t) can be chosen on occasion. For example, the total quantity can be, for example, 0.4, 0.5, 0.6, 0.7, etc. as a lower limit: it can be 1.6, 1.4, etc. as an upper limit. The value of xe2x80x9ctxe2x80x9d concerning Cu can be chosen in accordance with required cost of the hydrogen storage alloy, and Co quantities being contained in the hydrogen storage alloy, etc. The lower limit of the value of xe2x80x9ctxe2x80x9d can be, for example, 0.02, 0.05, 0.1, 0.2, etc. However, it is not limited to this region. According to the hydrogen storage alloy concerning the third aspect, based on Table 5 described later, as for xe2x80x9cqxe2x80x9d concerning Al, the lower limit of xe2x80x9cqxe2x80x9d can be, for example, 0.04, 0.05, etc. Also, as for xe2x80x9csxe2x80x9d concerning Mn, the lower limit can be 0.10, 0.14, etc. With an increase of the value of xe2x80x9cqxe2x80x9d and xe2x80x9csxe2x80x9d: namely, with an increase of Al quantity, or with an increase of Mn quantity, a hydrogen equilibrium pressure of the hydrogen storage alloy is generally decreased.
A preferable mode of the hydrogen storage alloy concerning the third aspect can satisfy at least one of the condition of (q greater than 0.06) and the condition of (s greater than 0.18). In this case, the hydrogen equilibrium pressure of the hydrogen storage alloy decreases by increasing of Al quantity and by increasing of Mn quantity. The preferable mode can satisfy both the condition of (q greater than 0.06) and the condition of (s greater than 0.18).
{circle around (4)} According to the hydrogen storage alloy concerning the first, the second, and the third aspects, since the conductive network is easily formed in the inside of the hydrogen storage alloy, conductivity of the hydrogen storage alloy increases, and internal resistance of the hydrogen storage alloy is reduced. In addition, since the conductive route becomes minute in the inside of the hydrogen storage alloy, the biased dispersion of current density is reduced in the hydrogen storage alloy. Also, the conductive network is composed of the second phase which can work as a catalysis for storing and emitting hydrogen. Therefore, the ability of hydrogen storage and hydrogen emission can be much improved. Especially, when the hydrogen storage alloy is used in low-temperatures such as winters, power can be improved,
(Invention of Producing Hydrogen Storage Alloy)
{circle around (1)} A process for producing hydrogen storage alloy concerning a fourth aspect, which comprises the steps of: employing a molten metal of one composition of hydrogen storage alloy concerning the above-mentioned aspects; solidifying the molten metal at a rapid cooling speed to form a solidified hydrogen storage alloy; and keeping the solidified hydrogen storage alloy at a range from 1000 to 1200xc2x0 C. for 30 minutes-120 hours to precipitate a second phase having a network state. Heating time can be chosen in accordance with size of the hydrogen storage alloy, etc. According to the process concerning the fourth aspect, when the molten metal solidified rapidly, alloying elements dissolve in supersaturation, and few or no second phase is precipitated; however, the second phase is effectively precipitated in the hydrogen storage alloy when it is heat-treated. According to the process concerning the fourth aspect, the conductive network, composed of the second phase being precipitated by heat treatment, is minute because the crystal grains are minutely generated by rapid solidifcaiton. Since the conductive network is minute, the process concerning the fourth aspect can reduce a biased dispersion of current density in the hydrogen storage alloy; therefore, it can contribute to uniform electric conductivity. In addition, the process concerning the fourth aspect can also contribute to improvement of the catalysis ability to suppress the partial over-charge and over-discharge when the hydrogen storage alloy is used in the battery. The process concerning the fourth aspect can use a molten-quenching method wherein molten metal is brought in contact with a rotor such as a cooling roller so as to form pieces or powder and that is well-known as rapid solidification. According to the process concerning the fourth aspect, a cooling rate may preferably be a speed over 104 K/sec, especially over 105 K/sec. As for the structure refinement caused by the rapid solidification, an average particle size and an average thickness of hydrogen storage alloy are preferably below 15 xcexcm, below 10 xcexcm, or below 5 xcexcm.
{circle around (2)} A process for producing the hydrogen storage alloy according to a fifth aspect, which comprises the steps of: employing a molten metal of hydrogen storage alloy having the composition concerning the above-mentioned aspects; solidifying the molten metal to form a lump body; crushing the lump body to form a crushed hydrogen storage alloy; and hydrogenating the crushed hydrogen storage alloy for further crushing. According to the process concerning the fifth aspect, since the molten metal of the alloy solidifies as the lump body such as an ingot, the solidification speed is not rapid. Therefore, the second phase forming the conductive network is precipitated by solidification. It is considered that the second phase is precipitated in a network state at a grain boundary of the hydrogen storage alloy phase. The process concerning the fifth aspect allows the hydrogenation for further crushing to be carried outxe2x80x94by storing and emitting hydrogen with respect to the crushed particles which is created by crushing the lump body. In this case, since the crystal lattice of the hydrogen storage alloy phase swells and contracts repetitiously by storing and emitting hydrogen; therefore, the hydrogen storage alloy phase becomes easy to be broken minutely. Therefore, the second phase having good conductivity, buried in the inside of the hydrogen storage alloy phase, is easily exposed at the outside of the hydrogen storage alloy phase by crushing. Exposing the second phase in hydogen storage alloy can increase electrical contact between the second phases in adjoining alloy powder so as to improve electrical conductivity in the hydrogen storage alloy. The powder crushed by the hydrogenation may be, for example, under 300 mesh (powder size: 45 xcexcm or less), or under 200 mesh (powder size: 75 xcexcm or less). xe2x80x9cUnder 300 meshxe2x80x9d means that powder passes through a 300 mesh.
(Invention of Hydrogen Storage Alloy Electrode, and Invention of Process for Producing Hydrogen Storage Alloy Electrode)
Hydrogen storage alloy electrode according to a sixth aspect, which is characterized by a material constituted by the hydrogen storage alloy having at least one composition of the above-mentioned aspects. According to this hydrogen storage alloy electrode, the second phase with the conductivity is formed in a network state to improve conductivity of the electrode itself and to improve power of the battery. Especially, the power of the battery can be improved in low-temperatures such as winters, etc. Also, when the battery is charged at high speed, the internal resistance of the electrode is reduced to decrease an exothermic reaction resulting from the internal resistance, and thereby the high-speed charging is much improved. In addition, since the electrically conductive network is minute, partial over-charge and partial over-discharge are effectively suppressed. The sixth aspect can use a system in which the powder of hydrogen storage alloy is combined with binder material, another system in which it is sintered by electrical welding, and another system in which it is sintered in a heat-treating furnace.
Hydrogen storage alloy electrode according to a seventh aspect, which comprises the steps of: employing hydrogen storage alloy having a powder shape and having a composition concerning one of the above-mentioned aspects; forming a mixture in which the hydrogen storage alloy and binder material are mixed; combining the mixture with a current collector to form a hydrogen storage alloy electrode. The mixture is generally slurry or paste. The conventional method can substantially be used in combining the mixture, having the form of slurry or paste, with the current collector. Therefore, the process concerning the seventh aspect can decrease the internal resistance of hydrogen storage alloy to increase conductivity, and it can use conventional equipment to suppress cost of equipment. The current collector is preferably porous. In this case, pores of the current collector are filled with the mixture.
A process for producing hydrogen storage alloy electrode according to an eighth aspect, which comprises the steps of: employing a hydrogen storage alloy having a powder shape and having a composition concerning one of the above-mentioned aspects; compressing the hydrogen storage alloy by press- working to form a compressed body without using binder material and without using a current collector; and sintering the compressed body to form a hydrogen storage alloy electrode. In the process concerning the eighth aspect, powder particles are directly connected, without using the binder material having difficulty in conductivity. Therefore, this aspect is advantageous in directly-connecting the second phases of the hydrogen storage alloy particle. So, conductivity of the boundary between particles is much improved: conductivity of the electrode is improved, and power of the battery is improved. Especially, power of the battery is improved in low-temperatures. Further, when the battery is charged at a high speed, the internal resistance of the electrode decreases to reduce an exothermic reaction resulting from the internal resistance; so, the high-speed charging of the battery is improved. The current collector may preferably be porous. This allows pores of the current collector to be filled with the mixture.
(Invention of Battery)
A battery according to the present invention comprises: a negative electrode generating a negative electrode reaction; and a positive electrode generating a positive electrode reaction, wherein the negative electrode is characterized by the hydrogen storage alloy having a composition concerning one of the hydrogen storage alloy concerning the above-mentioned aspects.
The battery concerning the present invention can improve conductivity of the negative electrode so as to improve power of the battery, while ensuring a hydrogen-storing ability and a hydrogen-emitting ability of the negative electrode. Especially, power of the battery can be improved, even in low-temperatures such as winters, etc. Also, when the battery is charged at a high speed, since the internal resistance of the electrode decreases to reduce an exothermic reaction, the high-speed charging of the battery is improved.
(Related Matter)
{circle around (1)} Since the hydrogen storage alloy is restricted in the above-mentioned composition, the second phase having good conductivity is easily formed in a network state in the inside of the organization. Therefore, the conductivity is improved in the hydrogen storage alloy. So, use of this hydrogen storage alloy as an electrode allows electric charges to be carried out quickly so as to obtain good conductivity. It is known that Ni has a catalyst ability in storing and emitting hydrogen in the hydrogen storage alloy. In the case where the second phase contains Ni, or in the case where the second phase is mainly composed of Ni, the second phase has a good catalyst ability to promote a hydrogen-storing reaction and a hydrogen-emitting reaction, and power is further improved. That is to say, the hydrogen storage alloy concerning the present invention has a hydrogen-storing ability and a catalytic ability for promoting the reaction. Especially, when the hydrogen storage alloy is used as the battery for electric automobile, power of the battery is improved by promoting hydrogen storage and hydrogen emission in low-temperatures so as to increase the high-speed charging of the battery.
{circle around (2)} The second phase, having good conductivity, of the present invention may generate the crystal structure having a Ni type or an AlNi3 type, or the crystal structure having a xcexc-NiMoCo type or a Co7Mo6 type.
Especially, the present inventor confirmed the hydrogen storage alloy by means of X-ray diffraction as follows: in the hydrogen storage alloy concerning the first aspect, it was confirmed that the second phase has the crystal structure having the Ni type or the AlNi3 type. In the hydrogen storage alloy concerning the second aspect, it was confirmed that the second phase has the crystal structure having the xcexc-NiNoCo type or the Co7Mo6 type. In the hydrogen storage alloy concerning the third aspect, it was confirmed that the second phase has the crystal structure having the Ni type or the AlNi3 type.
{circle around (3)} In the hydrogen storage alloy according to the present invention, a phase rate of the second phase is based on the above-mentioned composition. The phase rate may be, for example, 6-36 wt %. It is not limited to this region. xe2x80x9cXxe2x80x9d value (x=a+b+c+d) may be 3.9, 3.8 or less, and xe2x80x9cyxe2x80x9d value (y=i+j+k+l+m) may be 2.9, 2.8 or less, in such a manner that the second phase becomes 30% or less, and 33% or less in the hydrogen storage alloy by weight.
{circle around (4)} According to the hydrogen storage alloy concerning the present invention, the quantity of La being occupied in the misch metal (Mm) can be chosen on occasion. As described later, when the quantity of La (lanthanum) being occupied in the misch metal (Mm) closes to 100%, a hydrogen equilibrium pressure lowers. This can advantageously prevent an increase caused by repeated cycles in the internal pressure of the batteryxe2x80x94when the hydrogen storage is used in the battery.